Electrical heating systems may be utilized to supplement the heat provided by an engine and to heat the passenger compartment of a vehicle. While often used in electric vehicles powered solely by a traction battery and hybrid electric vehicles having an internal combustion engine in combination with a fraction battery, such heating systems may also be found in other applications. For example, electric heating systems may be utilized in air conditioners, dehumidifiers, dryers, portable heaters and other electrical appliances.
To provide passenger comfort in vehicle applications, vehicles have the capability to heat or cool the passenger compartment. Conventional vehicles use waste heat from the engine as the sole source of heating for the passenger compartment. With the advent of Battery Electric Vehicles (BEV), there is little or no waste heat available for use in heating the vehicle cabin. As such, BEVs may use an electric heater to warm the passenger compartment. Similarly, although Hybrid Electric Vehicles (HEV) include a small internal combustion engine that may provide some waste heat for heating the vehicle cabin, these vehicles are designed to minimize the use of the engine to maximize fuel economy. As such, these vehicles pose different heating challenges because the engine may not always be running and generating waste heat for use by the heating system. Plug-in Hybrid Electric Vehicles (PHEV) compound this issue by running with the engine off for significant periods of time. To provide optimal fuel economy benefits, it is desired to heat the passenger compartment without having to rely solely on engine waste heat.
As such, various alternatives have been developed to heat the passenger compartment of electric and hybrid electric vehicles. One such solution uses an electric heater as a heat source to provide heat for electric vehicles and/or supplement heat from the engine in hybrid vehicles when engine waste heat is insufficient to meet a heating demand for the vehicle cabin. In addition, electric and hybrid electric vehicles may use one or more mechanically and/or electrically driven actuators to pump coolant through the engine and/or electric heater. For example, such systems may include a main or primary water pump in addition to one or more auxiliary water pumps that may be utilized to circulate coolant through various coolant circuits whenever heating is required in the passenger compartment of a vehicle, or to heat other vehicle components. In particular, during vehicle operations where the engine is off, an auxiliary water pump may be utilized to pump coolant through the electric heater to a heater core to provide heat to the vehicle cabin.
Various commercially available actuators configured to circulate coolant may include some integrated diagnostic or self-test functions to determine operating state. However, these diagnostics may not be sufficient or suitable for some applications. In particular, integrated actuator diagnostics may not provide sufficient or timely feedback to determine whether the actuator is functioning as desired for a particular application. In vehicle applications, various operating conditions of the actuator may neither be observable by a controller nor communicated to the controller. For example, in one application, a simple low-cost interface between an actuator such as an auxiliary coolant pump and the controller that controls it is a single wire that has a low side driver in the controller for primary control and a low side driver in the actuator that may be used under certain operating conditions. The controller may be able to detect various operating conditions of the coolant pump, but may not detect an open ground to the simple actuator, for example. Similarly, the auxiliary pump may provide status information to the controller for various operating states, but not provide any indication of an open ground to the controller. As such, the controller may command the simple actuator on and even though the actuator does not actually operate, corresponding status information is not communicated back to the controller.